Sound is vibrations that travel through the air as a mechanical wave of pressure and displacement. Usually, sound refers to only those vibrations at frequencies that are within the range of human perception (generally 20 to 20,000 Hz). The frequency of sound relates to its pitch; the lower the frequency the lower the pitch. Sound waves are generated by a vibrating source (e.g. vocal cords, guitar strings, and an audio speaker diaphragm), which causes the adjacent air to vibrate. As the vibrations travel away from their source, they form a sound wave moving at about 1,125 feet/second.
As sound waves collide with objects, such as walls, the energy in the wave may be absorbed and/or reflected, in whole or in part. The interaction of a surface with sound waves varies according to the texture and structure of the surface. In general, soft, pliable, porous materials like fabric or fiberglass serve as good acoustic absorbers. Conversely, dense, hard, impenetrable materials (e.g. metals) reflect most sound energy. In between, rough materials may be used to scatter the sound energy (i.e. reflect in many directions). The nature of these absorptions, reflections and diffusions are critical to the auditory feel of a space. For example, when a sound wave strikes a flat, hard surface (such as the walls of a room), the sound is reflected in a coherent manner (provided that the dimension of the surface is sufficiently bigger than the wavelength of the incident sound). The sound waves that travel towards the reflecting surface are called the incident sound waves. The sound waves bouncing back from the reflecting surface are called reflected sound waves. In a room with reflecting walls, sound waves are arriving at the listener from a plurality of directions in and out of phase with other copies of the same sound wave. This results in degraded sound quality.
Another problem created indoors is parallel walls and standing waves. Standing waves occur when sound reflects off walls that are opposite each other and a wave equal to the distance between the walls is formed. Like any other sinusoidal wave, standing waves have high points, low points, and nodes. As you move around a room with standing waves you can hear as you walk through these high, low and dead points.
If you had the ability to reconstruct any particular space to improve its acoustic performance you might try to ensure that none of the walls are parallel to one another. However, merely making the walls a few degrees off from parallel is insufficient to fully eradicate standing wave problems. Yet, few spaces can afford the greater than 10 degree difference from parallel required to completely eradicate a standing wave problem. Still further, this non-parallel surface approach would not work well for the floor and ceiling pair.
One could alternatively try to reconstruct some particular space with dimensions that create modes, which would not interfere as much within the audible range. The formula for determining the fundamental frequency of a standing wave between two parallel walls for any particular room dimension is:f=V/d                 f=Fundamental frequency of the standing wave;        V=Velocity of sound (343 m/sec (1125 feet/sec));        d=dimensions (i.e. length, width, or height) of the room being considered in feetIn addition to a standing wave at the fundamental frequency of any room, other standing waves occur at harmonics of the fundamental frequency—that is 2, 3, and 4 times the fundamental frequency. So, for example, the foregoing equation shows that a 20 foot long room will cause resonances at the fundamental frequency of 56.25 Hz, as well as at, at least, 112.5 Hz, 168.75 Hz, 225 Hz, etc. These ‘resonant modes’ cause large peaks and dips in audible response, which begins for humans at as low at 20 Hz.        
Previously, audio engineers would try to add absorbent materials to an interior space to dampen these resonant modes. Absorbent materials merely decrease the amplitude of any acoustical anomalies, characteristics or other issues. The sound energy absorbed by the absorbent materials (or any other physical object within the space, for that matter) is transformed into heat and is said to have been “lost.” In particular, absorption is thought to occur through friction of the air motion against individual fibers of the absorbent materials with the resulting kinetic energy being converted to heat. Thus, the amount of sound energy lost is a function of frequency of the sound and the incident angle as well as the acoustic impedances of the air and of the object(s) involved in the absorption. Accordingly, the density of the absorbent material matters to the results. If the material is too loose sound will pass through practically unchanged, but too firm and reflection will occur. In addition, a layer of absorbent material has to be of the order of a quarter-wavelength thick in order to be effective. At low frequencies with their long wavelengths (i.e. the wavelength of a 20 Hz sound is nearly 60 feet) this requires a very thick layer of absorbent material.
Glass fibers are often used for absorption because of its useful physical properties. However, even six inches of glass fiber has little effect at 100 Hz, where a quarter wavelength is nearly 3 feet (i.e. 1125 feet per second/100 Hz). The effectiveness of glass fibers can improve above 100 Hz (the upper bass region) where 1 kHz has a quarter wave on the order of mere inches. Do-it-yourselfers sometimes use curtains and carpets for their allegedly absorptive properties to improve the sound quality in a room. However, these materials are really only effective for sound at frequencies above 5 kHz.
In addition to simple absorbent materials, various apparatuses to improve the acoustics of an interior space are known. Generally, these apparatuses have attempted to improve acoustics by controlling the sound wave absorption and reflection within the room by modifying the surfaces (e.g. walls and ceiling) of the interior space. For instance, audio engineers have added saw-toothed walls, sloping walls, multi-planar speaker soffits, bass traps, suspended clouds, Helmholtz resonators, quadratic diffusors, and the like to studios in an effort to achieve better acoustics. Even with these solutions, artists, producers and engineers alike were reduced to sharing a one-foot square sweet spot in even the most prestigious studio facilities. And worse, imaging, clarity, and realism still often lose out to economics and/or aesthetics. (Sweet spot is the position in the room where the audio sounds the best. Typically, a one foot cube at the mix position where frequency, amplitude and timber are as close to evenly balanced as possible.)
Thus, there is a need for apparatuses that improve the imaging, clarity, and realism of an interior space that are economical and aesthetically pleasing. There is an associated need for apparatuses that can be deployed in every home, office, theatre, store, plane, train and automobile to improve the acoustic properties of each of those spaces.
These and other objects and advantages of the present disclosure will also be apparent to those of ordinary skill in the art having the present drawings, specifications, and claims before them. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the disclosure, and be protected by the accompanying claims.